Freely mounted wheel set made of micro-machinable material and method of fabricating the same

Abstract

The invention relates to a gear train ( 51, 51 ′) including an arbour ( 53, 53 ′) a first end of which is fitted with an integral collar ( 52, 52 ′), a first wheel set ( 55, 55 ′) made of micro-machinable material being fitted onto the second end of the arbour ( 53, 53 ′). According to the invention, the gear train ( 51, 51 ′) includes a second wheel set ( 57, 57 ′) made of micro-machinable material, which is independent of the movements of said first wheel set and which includes an aperture ( 58, 58 ′) whose wall is mounted opposite said arbour so that the second wheel set ( 57, 57 ′) is freely mounted on said first end of the arbour ( 53, 53 ′).

What is claimed is: 
     
       1. A method of fabricating a gear train, the method comprising the following steps:
 a) providing a substrate that includes a top layer and a bottom layer made of micro-machinable material, wherein the top layer and the bottom layer are secured to each other by an intermediate layer; 
 b) etching at least one pattern in the top layer and the intermediate layer until the bottom layer is exposed, wherein etching the at least one pattern forms at least one first cavity belonging to a first wheel set; 
 c) coating at least the bottom of the at least one first cavity with an electrically conductive coating; 
 d) electroforming a material, at least in the bottom of the at least one first cavity; 
 e) etching a second pattern in the bottom layer as far as the coating of the electrically conductive material, wherein etching the second pattern forms at least one second cavity belonging to a second wheel set; 
 f) structuring a photosensitive resin on the bottom of the bottom layer, wherein the photosensitive resin forms a sheathing on the walls of the at least one second cavity and at least one recess, wherein the photosensitive resin that flares out coaxially from the at least second cavity; 
 g) continuing the electroforming started in step d) to fill the at least one first cavity and starting to electroform a material in the at least one second cavity and the at least one recess, wherein the electroforming forms an arbour fitted with a collar; 
 h) removing the photosensitive resin; 
 i) removing the intermediate layer, wherein removing the intermediate layer separates the first and second wheel sets; and 
 j) releasing the fabricated wheel set from the substrate. 
 
     
     
       2. The method according to  claim 1 , wherein step f) also includes the following phase:
 k) coating at least the bottom of the at least one recess with a second electrically conductive coating to improve the forming of the collar. 
 
     
     
       3. The method according to  claim 1 , wherein prior to step d), the method includes the following step:
 l) mounting a part on the top of the substrate, wherein mounting the part forms at least one other recess that flares out coaxially from the at least one first cavity, wherein mounting the part provides a level of electroformed material above the top layer. 
 
     
     
       4. The method according  claim 3 , wherein step c) also allows at least the bottom of the at least one other recess to be coated with the electrically conductive coating. 
     
     
       5. The method according to  claim 1 , wherein, after step c), the method includes the following step:
 m) mounting a pin in the at least one first cavity, wherein mounting the pin forms a hole in the future gear train. 
 
     
     
       6. The method according to  claim 1 , wherein, prior to step g), the method includes the following step:
 n) mounting a pin in the at least one second cavity, wherein mounting the pin forms a hole in the future gear train. 
 
     
     
       7. The method according to  claim 1 , wherein steps b) and e) include the following phases:
 structuring at least one protective mask on the layer to be etched; 
 performing an anisotropic etch of the layer over the parts that are not covered by the at least one protective mask; 
 removing the mask. 
 
     
     
       8. The method according to  claim 1 , wherein several gear trains are fabricated on the same substrate. 
     
     
       9. The method according to  claim 1 , wherein each coating includes at least one gold layer. 
     
     
       10. The method according to  claim 1 , wherein the micro-machinable materials are silicon-based.